Molding masses for producing fiber reinforced plastic articles, methods of preparing such molding masses, and articles produced therefrom

ABSTRACT

A molding mass is obtained by adding to a thermosetting resin, for example, a polyester or epoxy resin, in liquid state, a particulate filler material, such as an asbestos or quartz powder, and bundled together reinforcing fibers of inorganic material, such as, glass fibers, which fibers have a diameter in the range from 0.01 to 0.02 mm and a length to diameter ratio between approximately 100 and 500, with the particle size of the filler material varying between 5 and 50 Mu in direct proportion to the variation of the length to diameter ratio, and subjecting the molding mass to a continuous mixing and kneading action at a localized region and removing one-fourth to one-seventh of the mass transported to the outlet of this region by means of a conveying ribbon and recycling the removed mass to the localized region, the rest of the transported mass being passed out of the mixing zone, thereby to avoid a substantial temperature rise in the mass while the mixing and kneading is continued until the mass has a density of 1.5 and at least approximately 80 percent of the bundled together fibers are pulled apart into individual fibers dispersed uniformly throughout the mass.

ilnited States Patent Van Herpt 51 June 6, 1972 54 MOLDING MASSES FORPRODUCING 2,819,243 l/1958 Baker ..260/40 gARING FOREIGN PATENTS ORAPPLICATIONS 9 t H 64,634 4 1943 Norway .259 10 SUCH MOLDING SSES AND64,634 4/1943 Norway ..259/10 ARTICLES PRODUCED THEREFROM [72] Inventor:Cornelis Hendrikus Jozephus Van Herpt,

Helmond, Netherlands [73] Assignee: N. V. Koninklijke, Helmond,Netherlands [22] Filed: May 18, 1970 [21] App]. No.: 37,456

Related U.S. Application Data [63] Continuation of Ser. No. 723,225,Apr. 22, 1968, abandoned, which is a continuation-in-part of Ser. No.512,141, Dec. 7, 1965, abandoned, which is a continuation-in-part ofSer. No. 304,462, Aug. 26, 1963, abandoned,

[30] Foreign Application Priority Data Sept. 7, 1962 Netherlands..2s302o Aug. 8, 1963 Netherlands ..282776 Mar. 9, 1965 Netherlands..6502959 [52] U.S. Cl. ..260/37 EP, 260/40 R [51] 1nt.Cl ..C08g51/04[58] Field of Search ..260/37 R, 37 EP; 259/10 [56] References CitedUNITED STATES PATENTS 2,819,243 9/1958 Baker ..260/40 PrimaryExaminer-Morris Liebman Assistant ExaminerS. M. Person Attorney-ArnoldRobinson ABSTRACT A molding mass is obtained by adding to athermosetting resin, for example, a polyester or epoxy resin, in liquidstate, a particulate filler material, such as an asbestos or quartzpowder, and bundled together reinforcing fibers of inorganic material,such as, glass fibers, which fibers have a diameter in the range from0.01 to 0.02 mm and a length to diameter ratio between approximately 100and 500, with the particle size of the filler material varying between 5and 501.1. in direct proportion to the variation of the length todiameter ratio, and subjecting the molding mass to a continuous mixingand kneading action at a localized region and removing one-fourth toone-seventh of the mass transported to the outlet of this region bymeans of a conveying ribbon and recycling the removed mass to the 10-calized region, the rest of the transported mass being passed out of themixing zone, thereby to avoid a substantial temperature rise in the masswhile the mixing and kneading is continued until the mass has a densityof 1.5 and at least approximately 80 percent of the bundled togetherfibers are pulled apart into individual fibers dispersed uniformlythroughout the mass.

2 Claims, 3' Drawing Figures I minutes temp.

INVENTOR.

PATENTEDJUN 6 I872 SHEET 2 BF 2 INVENTOR.

MOLDING MASSES FOR PRODUCING FIBER REINFORCED PLASTIC ARTICLES, METHODSOF PREPARING SUCH MOLDING MASSES, AND ARTICLES PRODUCED THEREFROM Thisapplication is a continuation of my application Ser. No. 723,225, filedApr. 22, 1968, which was a continuation-inpart of application Ser. No.512,141 filed Dec. 7, 1965, which was a continuation-in-part ofapplication Ser. No. 304,462, filed Aug. 26, 1963, all now abandoned.

lt has been known to provide a molding mass composed of a mixture of athermosetting resin, such as, polyester or epoxy resins, and mineralreinforcing fibers and fillers, which mass remains kneadable or plasticfor some time after the mixing together of its constituents and isthereafter solidified by exposure to a considerably higher temperature.

However, molding masses constituted as above do not often producesatisfactory reinforced plastic articles, particularly when the latterare formed by injection molding of the mass. Defects in the moldedarticles are especially found to exist when the reinforcing fibers areintroduced in to the molding mixture in the form of bundles of adheringglass fibers which resist separation into individual fibers that can beuniformly distributed throughout the molding mass.

The presence of non-homogeneously distributed fibers can easily giverise to the formation of cracks in the molded articles and to corrosionby chemical agents, especially after surfaces of these articles havebeen machined. On machining these surfaces, the glass fiber bundlesbecome exposed and acids or other corrosive chemical agents may easilypenetrate therealong into the article giving rise to bad corrosion.

It is well known in the art that a thermosetting resin together with acuring agent will cure after a given time which depends on thetemperature of the mass. Obviously the setting time is low for a hightemperature and high for a low temperature.

The setting times can be derived from FIG. 2 which shows therelationship between temperature of the molding mass and the potlife (orsetting time). In order to obtain a suitable mass the mixing procedureshould be effected in a relative short period without increasing thetemperature to a high value.

Although it has been suggested to avoid the above disadvantages-bysuitable selection of the diameter of the fibers to a viscosity thereofthat is sufficiently high to permit the bun- I dles of reinforcingfibers, corresponding to at least 35 percent by weight of the resin, tobe pulled apart into individual fibers by a mixing and kneading action,and in that such mixing and kneading action is applied continuously atonly a portion of the total mass which is circulated so as to berepeatedly and intermittently subjected to such action, whereby thetemperature of the mass, during mixing and kneading, does not riseconsiderably even in the absence of external cooling or the introductionof cooling agents into the mass. 7

The avoidance of an excessive temperature rise in the mass during themixing and kneading thereof in the manner described above is preferredover the use of external cooling or the introduction of cooling agentsinto the mass in that the cooling effect of external cooling or coolingagents can never 7 uniformly affect the mass with the result thatlocally too high temperatures are produced during the mixing process.Such local hot spots give rise to partial polymerization orprepolymerization of the resin, so that portions of the mass have toohigh a viscosity and, owing thereto, there is a non-uniform distributionof the individual glassor reinforcing fibers or the like in the resinmass.

The mixing and kneading action according to the invention is continueduntil at least percent of the fibers are separated from each other.

A sufficiently high viscosity of the mixture of liquid resin and fillerfor separating the bundles of reinforcing fibers by the mixing andkneading action is obtained when the amount of filler is betweenapproximately 80 and 150 percent, by weight, of the amount of resin.

In the case of a mass for injection molding of articles, the amount offiller is preferably I25 percent by weight, of the amount of polyesterresin, and preferably 103 percent, by weight, of the amount of epoxyresin.

Heretofore, the reinforcing fibers used in injection molding masses havebeen in the form of so-called shopped strands, that is, bundles eachconsisting of a plurality of, for example, 100, fibers which sticktogether by means of their adhesive properties. Usually such reinforcingfibers have a length of 6 .mm and a diameter of substantially 0.25 mm,so that the ratio between the length and the diameter, that is, theso-called l/d ratio, for each of these pieces is approximately 25. Ithas been found, quite surprisingly, that the l/d ratio of thereinforcing fibers in the injection molding mass is of great importancewith respect to the possibility of forming an injection molding mass ofhigh quality and especially one affording great bending strength toarticles manufactured of this injection molding mass.

In order to obtain the desired results, it has been found that thesocalled l/d ratio for each reinforcing fiber has to be predetermined sothat this ratio will vary between 100 and 500, preferably in a directproportional ratio to the dimensions of the particles forming the fillermaterials, which dimensions can vary from 5 to 50p. Further, at least 80percent and preferably at least percent, of the quantity of reinforcingpieces mixed into the injection molding mass should be single fibershaving a diameter varying between 0.0l and 0.02 mm. When employing theaforementioned ratios, an injection molding mass is obtained in whicheach fiber is embedded completely in the base resin, and the fibers arespread or oriented in all possible directions in the mass. Further, suchinjection molding mass is capable of filling the injection molds evenwhen the latter have narrow passages or channels and the reinforcingfibers remain uniformly dispersed throughout the mass and do not collector jam in the narrow passages of the mold.

In accordance with this invention, the reinforcing fibers included in aninjection molding mass preferably have a length that is less than theminimum dimensions of the articles to be molded therefrom at thenarrowest cross-sections of the mold cavity.

The mixing and kneading process should be performed in such a way thatone-fourth to one-seventh of the mass conveyed to the oultet is removedand recycled to the open mixing zone, the remainder of the transportedmaterial being moved out of the mixing and kneading area. This resultsin tearing forces, whereby the bundles of inorganic fibers can be tornapart by relatively small forces applied in the mixing and kneading areaor zone.

A molding mass having the previously described characteristics inaccordance with the invention is preferably produced by introducingrequired quantities of a base resin, filler materials and reinforcingfibers into the mixing chamber of a mixing device; rotating a mixingscrew consisting of a conveying band wound spirally about a shaft andmounted in the chamber of the mixing device; the rotated mixing screwkneading and mixing the materials introduced into the mixing chamber toform an injection molding mass and, at the same time, driving the mixedmass continuously forward over an upwardly inclined portion of thebottom of the chamber toward an opening leading into a tubular outletpiece integral with the mixing chamber; rotating a conveying screwmounted inside the tubular outlet piece and having a capacity adapted totransport to the outside only one-fourth to one-seventh part of the massforced continuously to the mouth of the outlet so that only part of thearriving mass is discharged through the tubular outlet, whereas the restis forced in an upward direction in the mixing chamber and returns in asubstantially horizontal plane above the mixing screw, that is, out ofthe mixing and kneading area, to the inlet end of the latter where it isagain subjected to the kneading and mixing process; and carrying on thewhole process continuously until all the materials introduced into themixing chamber are formed into an injection molding mass havingseparated reinforcing fibers and passed out of the mixing device throughthe outlet piece.

Since only a part one-fourth to one-seventh of the mass arriving at themouth of the tubular outlet is discharged therethrough and the remainderof such mass is recirculated out of the mixing and kneading area, suchrecirculated mass is allowed to cool and the mass in the mixing chamberdoes not undergo a considerable rise in temperature. Further, by reasonof the presence of the stated amounts of fillers in the molding mass,the viscosity of the latter is sufficient to cause shearing forces toarise for easily tearing apart the bundles of reinforcing fibers,particularly when part of the mixed mass is removed from the mixing andkneading area as aforesaid.

The mixing process embodying this invention is preferably performed in amixer of the type illustrated in the drawing which shows a perspectiveview thereof, partly broken away and in section.

Each mixer consists of a mixing vessel 1 and opening, at one end, intoan outlet duct 3. A helical ribbon 6 is fixedly secured to a shaftwhich, at one end, is rotatably supported in an end wall 4 of the mixingvessel 1. The part of the shaft extending in the duct 3 has a conveyorworm 7 thereon. The bottom 8 of the mixing vessel 1 merges through agently upwardly inclined portion 9 into the bottom 10 of the duct 3. Thehelical ribbon 6 is connected through a similarly tapering portion 11with the conveyor worm 7. The construction is such that the taperingportion 11 conforms to the gently upwardly inclined portion 9 of thebottom of the mixing vessel 1. Disposed at the outside of the mixingvessel 1 and connected to the shaft 5 is a transmission 12 which isdriven by an electric motor (not shown) accommodated in a housing whichis provided with cooling ribs. The endwall 13 must be substantiallyvertical. The mixer employed has the following dimensions. The width Aof the open mixing vessel 1 is 180 mm, the length B is 230 mm. Thelength C at the location of the bridge piece is 70 mm.

The length D of the outlet 3 is 80 mm, while the inner diameter E of theoutlet is 75 mm. The pitch F of the conveyor worm 7 is 50 mm, while thepitch S of the ribbon 6 has a value of 140 mm. The shaft 5 has adiameter G of 50 mm and at the location of the outlet is reduced to Hmm. The ribbon 6 has a width K of 8 mm. The diameter N ofribbon 7 is 180mm, e.g. glass fiber bundles, required in order to prepare the ejectionmolding mass are introduced into the mixing vessel of the mixer,whereupon due to the rotation of the shaft 5 mixing is started. Underthese circumstances the ribbon 6 with the bridge piece 1 conveys in thedirection of the outlet 3. The conveyor worm 7 provided in the outlet 3can however only take along one-fifth part of the mass supplied to theoutlet 3 and discharge same from the mixer. The greater part, fourfifthsof the supplied material is, however, passed in the direction of thearrow P and outside of the mixing and kneading area.

The tapering portion 11 of the mixing and kneading member in cooperationwith the inclined portion 9 of the bottom of the mixing vessel 1prevents the mass from caking at the entrance or mouth of the duct 3.Due to the exerted forces, a plucking action is produced on the glassfiber bundles on stirring the mass, with the result that individualglass fibers are obtained. It is obvious that during the mixing processthe mass is repeatedly moved out of the mixing and kneading area and isalso repeatedly subjected to the mixing and kneading operation. The partdischarged from the mixer is recycled to the mixer (arrow M). The ratiobetween the discharged material and the material being transported tothe outlet of the mixing zone is called recycle ration.

In the following specific examples, Examples 1, 2 and 10 illustratedifiiculties encountered when proportions of the injection molding massdo not conform to ranges according to this invention, the other examplesare illustrative of the invention.

EXAMPLE 1 Into a mixing device as described hereinbefore are introduced1 kg of polyester resin and 1 kg of asbestos filler with a particle sizeof approximately 50;.t. After mixing for 10 min with care in the deviceand discharging one-fifth of the mass moved to the outlet and recyclingsaid part of the mass to the mixer while adding a suitable catalyst,such as, 2 percent of benzoyl peroxide, a number of test bars having aflexural strength of 458 kg/cm are made. Owing to the lack ofreinforcing fibers these bars are weak, indicating that the molding masscannot be applied to the manufacture of articles that need to be of highstrength, such as pump housings and the like.

EXAMPLE 2 Introduced into the device, as in Example 1, are 1 kg ofpolyester resin and 0.45 kg of glass fibers, the latter in the shape offiber bundles with a fiber length of 6 mm and an individual fiberdiameter of 0.015 mm. The catalyst, as mentioned in Example 1 is addedwhile mixing is performed for 15 minutes. (recycle ratio 1 5). Thereuponthe test bars are made which, under circumstances analogous to those ofExample 1, appeared to have a flexural strength of 605. On examination,the glass fibers are seen to be incompletely distributed owing to whichthe mass is neither fit for the manufacture of injection moldedarticles.

EXAMPLE 3 In accordance with this invention 1 kg of polyester resin 1.25kg of asbestos (density 1.4) with a particle size of 50 microns and 350grams of shopped strands of glass fibers with a length of 6 mm arecontinuously introduced into the mixer. After admixing 2 percentbenzoylperoxide (calculated on the resin) the mixer is started. Theproduct discharged by way of the outlet 3 (recycle ratio of 1 5) isagain manually introduced into the mixing vessel until the density ofthe mass amounts to 1.3 and the temperature to 33", (after 8 minutesmixing). Test bars can be made of this material having a flexuralstrength of 1,120. The same values were attained when the mass was mixedto a volume weight of 1.5 and a temperature of 36 C, (after 1 1 minmixing). The fibers are extraordinarily well distributed in this mass.

If a mixer is applied with a discharge ratio or recycle ratio of 1 7 thetemperature on obtaining a density of 1.3 has already risen to 52 Cwhereby owing to the increase of the viscosity during mixing for 8minutes the fibers are not evenly distributed. The flexural strengthamounts only to 1,000 kg/cm.

A mixer with a discharge ratio of l 3 has the drawback that no adequatemixing is achieved and in this way neither the required volume weight of1.3 nor a proper distribution of the fibers can be achieved after 25minutes. The temperature of the mass amounts to 30 C. Test bars have aflexural length of 760 kg/cm".

EXAMPLE 4 a. Introduced into a mixer of the aforementioned type are 1 kgepoxy resin, 0.50 kg asbestos with a particle size of 50 microns and0.35 kg glass fibers in bundles with a length of 6 mm and a diameter of0.01 5 mm. After adding a mixture of 65 parts of D.D.M. hardener and 32parts of M.P.D. hardener, the mixture amounting to 20 percent of thetotal quantity of resin, mixing is effected at a discharge ratio of 1 5while the discharged material is recycled. After having obtained adensity of 1.4 after 10 minutes and a temperature of 38 C test bars aremade, the flexural strength of said bars range from 1,420

to 1,450. This mass is satisfactory but not suitable for injectionmolding as the distribution of glass is only 80 percent and the workingproperties bad.

b. On mixing with a discharge ratio of 1 3 the glass fibers are notevenly distributed after mixing for 25 minutes and in that case testbars with a flexural strength of 780 are obtained surfaces have manypores owing to the bad distribution of the fibers.

EXAMPLE 5 In the event that the conditions of Example 4a are maintainedand only the lengths of the reinforcing fibers are varied, the followingresults are obtained:

Fiber Length of Test Bars EXAMPLE 6 When the glass fibers are replacedby brayed glass made up of 56 parts of glass powder and 44 parts ofglass fibers, the lengths of the powder particles and fibers being inthe range of 0.4 and 3.0 mm., for each 100 parts, by weight, of resin, a8, of 830 was found when the aforementioned hardeners were employed.

EXAMPLE 7 a. A very good mixture has been obtained from 100 parts ofepoxy resin, 32 parts of bundles of glass fibers having a length of 6 mmand a diameter of 0.015 mm average, and 103 parts of asbestos'powderwith a particle size of 5011., to which mixture 20 parts of acomposition of 65 parts of DDM hardener and 32 parts of MPD hardenerwere added. After mixing for minutes with a recycle ratio of 1': 5 thefinally obtained mass is a flaky one which, however, can be suitablyworked up in the injection molding process. The density is 1.45 and thetemperature 40 C. 98 percent of the glass fibers are divided as singlefibers after mixing for 8 min, the temperature of the mass being 42 C.The flexural strength amounts to 1,300 kg/cm". Similar results areobtained with 30 parts of bundles of glass fibers but the flexuralstrength is percent lower.

b. At a recycle ratio of l 7 the final mass had a temperature of 68 C ata volume weight of 1.5 and a mixing time of 10 min. The fibers are onlyfor 76 percent divided into single fibers. At a volume weight of 1.3 thetemperature is already 65 C and the fiber distribution comprises about72 percent single fibers. The flexural strength is 1,100.

c. At a discharge ratio of l 3 only 50 percent of the fibers in thefinal mass, are divided into single fibers after mixing for minutes. Theend temperature being 36 C.

d. In this example the method according to Example 7a was continuouslyperformed. For that purpose three mixers were disposed above one anotherin such a way that the outlet of the first mixer is situated over themixing vessel of the second mixer, while the outlet of the second mixeris situated over the mixing vessel of the third mixer. At first themixing vessel of the first mixer is filled with 1 kg epoxy resin(Bayer), 3.2 kg glass fibers in bundles, 1.03 kg asbestos powder of 50microns. With a recycle ratio of 1 5 the end temperature of the mass is42 C. Then the first mixer is started and reagents added in the amountin order to have a constant quantity of materials in the first mixer.After having filled the second mixer, this mixer is started and so on.The mass discharged from the third mixer is recycled to the first mixer,the supply of reagents being controlled in order to have a constantquantity in the first mixer, until an amount corresponding to the volumeof the first mass has been recycled. Further recycling is not necessary.

e. The quality of injection molded articles obtained from the injectionmolding mass having epoxy resin as its base, for example, as in Examples3 and 7 above, is shown by immersing test bars molded of such mass in 30percent muriatic acid for a period of 10 hours. The test bars have aninitial flexural strength of 1,120 1,400 kg/cm and the change inflexural strength, at the conclusion of the treatment, is dependent onthe temperature of the muriatic acid, as follows:

Flexural strength after Temperature of muriatic 10.000 hours (kg/cm)acid C.

Example 4 Example 7 Further, the test bars were found to undergo thefollowing small increases in weight after immersion in muriatic acid atvarious temperatures:

Time of treatment Temperature of muriatic acid Weight increase 10.000hrs 25 C. 0.1% 7.000 his 70 C. 1.0% 1.000 hrs 90 C. 1.0%

EXAMPLE 8 EXAMPLE 9 A reinforced plastic article having a minimumcross-sectional dimension of 3 mm, is injection molded from the massproduced according to Example 3 or 4 (that is, having a fiber length of6 mm.). The molded article is found to have many cracks in the region ofits narrowest cross-section. Such cracks are avoided when the moldingmass is formed with glass fibers having a length of 3 mm that is, notgreater than the minimum cross-sectional dimension of the moldedarticle.

Further, the flexural strength of the article molded of a mass havingreinforcing fibers of 3 mm length is increased approximately 20 percentwhen the filler material, which has a particle size of 50 microns inExample 3 or 4 is replaced by a filler material of 20 microns particlesize. This demonstrates the advantage of varying the l/d ratio of theglass fibers in proportion to the particle size of the filler material,as in accordance with this invention.

EXAMPLE 10 A very good mixture has been obtained from parts by weight ofpolyester resin, 100 parts by weight of asbestos powder with a particlessize of approximately 50 microns, 30 parts by weight of glass fibershaving a length of 6 mm and an average diameter of 0.015 mm, and 25parts, by weight of quartz powder of a particle size of 30 microns.After adding 2 percent of benzoyl peroxide as a catalyst this mass ismixed with a recycle ratio of 1 5. The finally obtained mass is verysuitable for injection molding. Test bars have a flexural strength of1,300.

EXAMPLE 1] Introduced into the mixer, as in Example 1 are 1 kg of aphenol formaldehyde resin (Novolak), 1 kg of asbestos with a particlesize of 50 microns and 350 grams of glass fibers with a length of 6 mmand an average diameter of 0.015 mm. After adding an appropriate amountof hexamethylenetetramine the mass is mixed and used for injectionmolding. The amount of hexamethylenetetramine depends on the quality ofthe resin and the desired properties of the molded article.

Although specific examples of the invention are described herein, it isto be understood that the invention is not limited to those preciseexamples which are merely illustrative.

What is claimed is:

l. The method of preparing an injection molding mass comprising thesteps of:

a. admixing a mixture consisting essentially of a thermosetting resinselected from the group consisting of polyester resins and epoxy resinsin the liquid state and approximately 80-100 percent by weight of theresin of a particulate filler material with a specific gravity fromabout 2.1 to about 2.8 and with a particle size ranging from about toabout 50 microns;

b. admixing with said resin and filler, from about 30 to 35 percent byweight of resin of glass fibers, each of said fibers having a diameterof from about 0.01 mm to about 0.02 mm and a length/diameter ratio fromabout 100 to about 500 thereby to form a mass consisting essentially ofsaid resin, said filler and said fibers;

c. mixing said mass in an open top mixing zone by means of a rotatingribbon conveyor, said conveyor being entirely covered by said mass;

d. transporting the mass by means of the ribbon conveyor through atubular outlet piece integral with the mixing chamber, said tubularoutlet piece being of substantially uniform cross section and beingcapable of discharging about one-seventh to about one-fourth of saidmass;

e. discharging the about one-fourth to about one-seventh of the massheld in the tubular outlet piece;

recycling the about one-fourth to about one-seventh of the massdischarged;

g. continuing the mixing in the mixing zone until the mass has anaverage density of at least 1.3 and at least percent of all fibers areindividual fibers; and

h. wherein the temperature throughout the mass during mixing is at alltimes below about 50 C. thereby maintaining the mass in a substantiallyunreacted condition.

2. Method according to claim 1 wherein mixing is continued until themass has an average density of 1.5

2. Method according to claim 1 wherein mixing is continued until themass has an average density of 1.5.